In a process of cutting a silicon ingot in order to manufacture a silicon wafer for a semiconductor and a solar cell, a wire saw has been generally used. Here, the wire has a diameter of about 0.14 μm, and sludge for cutting that contains silicon carbide (SiC) having an average particle size of 20 μm has been used. In most of the domestic silicon wafer manufacturing process, sludge containing a large amounts of SiC, silicon particles, cutting oil, and the like, has been generated, and all of this sludge was buried underground by waste disposal company until a few years ago. However, processed sludge in which an abrasive material and the cutting oil are mixed with each other contributes to about 68.1% in view of cost of a silicon wafer processing process. Therefore, a technology of separating/recovering SiC having an average particle size of 20 μm and the cutting oil that are included in the silicon sludge to reuse in a silicon wafer cutting process has been developed and has been used. However, even in the case in which reusable components is separated/recovered from the sludge generated as describe above to thereby be reused, it was known that an amount of waste sludge remaining as a final residue to be discharged has grown to about 21,000 tons per year, based on 2010, and in accordance with rapid growth of a photovoltaic silicon wafer industry, generation of the waste sludge will also correspondingly increase.
Since the sludge generated at the time of manufacturing a silicon wafer is classified as a specified waste, the sludge may not be treated by simply burning nor be simply buried due to the cutting oil component contained in the sludge. However, in the case in which useful components contained in the sludge may be effectively separated/recovered, SiC may be used as a raw material of a ceramic such as a high temperature refractory, a silica composite, or the like, and silicon powders may be used as a synthetic material of high purity silicon compounds and be used to manufacture a poly-silicon at the time of ultra-high purification. In the silicon sludge, although slightly different according to companies, generally silicon, SiC, and an oil component used as the cutting oil are mixed. Therefore, in order to effectively separate these materials and make products, a liquid and a solid should be efficiently separated. In the silicon sludge, small amounts of additives and metal components may be included as well as the cutting oil and the abrasive material, and particularly, in the case of oil components, which are liquid components, by-products having a low thermal stability may be easily generated in a purification process. Therefore, in order to purify the oil component from the silicon sludge and utilize the solid component as the ceramic material, a heat treatment technology of efficiently removing the oil component such as ethylene glycol and a technology of controlling and separating trace components such as the additive and metal should be developed. In the silicon sludge from which the oil component and metal component are removed, silicon and silicon carbide particles remain, and in the case in which these two kinds of particles are efficiently separated, the silicon particles and the silicon carbide particles are obtained. These particles may be used as raw materials of various materials such as silicon compounds, structural ceramics, and the like.